Liquid optically clear adhesives (LOCA) are becoming more prevalent in the display industry to fill the air gap between the optical elements. For example, LOCAs can fill the air gap between a cover glass and indium tin oxide (ITO) touch sensors, between ITO touch sensors and a liquid crystal module, or directly between the cover glass and the liquid crystal module. Recently, several coating processes have been developed for more precisely coating patches of low to moderate viscosity, self-leveling liquids, such as liquid optically clear adhesives (LOCA), onto substrates.
One known process for applying LOCA patches to a substrate makes use of flowable liquid OCAs that behave like low viscosity Newtonian liquids at the application conditions. To prevent flow beyond the desired printing area due to self-leveling of these liquids, the use of a pre-cured dam material (matching the refractive index of the LOCA) is often required. This involves an additional process step, and may still potentially lead to overflow of the LOCA if a sufficiently precise amount is not dispensed and/or there is not perfect co-planarity between the two substrates that are being bonded with the LOCA.
The use of a screen for precise printing LOCA patches has also been described, for example in Kobayashi et al. (U.S. Patent Application Pub. No. 2009/0215351). Additionally, the use of a stencil for precise printing of LOCA patches has been described in PCT International Pub. No. WO 2012/036980. Regardless of whether a screen or a stencil is used, self-leveling of the low to moderate viscosity LOCA may degrade the desired positional accuracy of the LOCA patch placement on the substrate. Nevertheless, such adhesives and processes have been found useful in forming optical assemblies for producing display panels used in a variety of electronic devices.